Power distribution networks, such as the UK's National Grid, can supply electricity to millions of homes and businesses. Power distribution networks are typically supplied with electricity by a combination of many different power generation techniques, from many different power stations, spread across large geographical areas.
Power stations supplying a network can generally be divided into two groups: 1) the “core network” of always-on power stations, and 2) the “response network” of power stations which can be turned on, off, or significantly vary their output, to respond to variance in power demand. Nuclear and coal-fired power stations are typical “core network” power stations as they take a considerable time to start and stop. Hydro-electric and gas-fired power stations, which can start generating power within minutes of receiving a request, are typical “response network” power stations.
Demand for power across a network is not constant and is influenced by many different factors. The factors include the time of day, the time of year, the weather and even the timing of national sporting events. Whilst the future demand on a power network can (to a certain extent) be predicted by analysing real time data services such as the Balancing Mechanism Reporting System (BMRS), weather forecasts and predictions from national bodies, unexpected surges in demand are a very common occurrence.
If the power network cannot meet surges in demand, power blackouts can ensue. Additionally, power blackouts can occur if the frequency of the network is too high. The level of demand on the power network effects the speed of rotation of the generators connected to it, and hence the frequency of the electricity across the network. As demand drops, the loads on the generators drop, causing the generators to spin faster and the frequency to increase. If the generators spin too fast they will automatically trip out for their protection, causing power blackouts. Power blackouts can cause significant damage to electrical equipment and can shut down factories with resultant damage to the economy as a whole.
Typically, to meet surges in demand, operators of power distribution networks will issue demand response event notices, such as a “Fast Reserve Despatch” notice. Such event notices generally state at least: the amount of power the distribution network needs adding or removing, the estimated time this power needs to be added or removed, and the required response time. In order to service these requests, significant power generation capability must be kept ready at all times.
Due to the difference in power generation technology response times and longevity, many different power generation technologies must be kept ready. For example, a hydro-electric dam may be able to start generating power within minutes, but the dam can produce power for only a finite time. Whereas, an oil-fired power station may take 20 minutes to start but can generate power indefinitely.
Having large amounts of power generation capacity sitting idle whilst waiting for peaks in demand is both expensive and inefficient. Due to advances in energy storage, there is an increasing pool of devices connected to the power generation network which are capable of providing significant amounts of power. Examples of such devices include electric vehicles (EVs), uninterruptible power supplies (UPSs) and photovoltaic storage banks (PVs).
Since many of these devices are connected both to the power distribution network and the internet (so called “smart devices”), it is possible to remotely control these devices to charge and/or discharge some of their capacity as needed. To make a significant contribution to a large scale power distribution network, the simultaneous use of thousands of devices is required. However, there are considerable difficulties in efficiently using so many devices.
For example, owners of electric vehicles do not mind at what time of the day the vehicle battery is charged, or if a proportion of its battery capacity is discharged, as long as the electric vehicle is ready to use when needed. Typically, electric vehicles across the country are plugged in at a similar time of evening, creating a surge in power demand on the network. If the charging of these devices could be centrally coordinated, the batteries could start charging at staggered times throughout the night, reducing any spike in demand. Furthermore, if an unexpected demand for power occurs on the network, a proportion of the energy stored across the combined electric vehicle fleet could be used to supply the network, meeting the unexpected demand,
Similarly, photovoltaic systems can be used to charge banks of batteries for use when the sun is not shining. Owners of PV's may be happy to distribute excess power generation capacity when they are not using it, as long as their needs are met when they need more power.
Typically, prior art power distribution networks maintain information about the state of every device they control, requiring huge amounts of computational processing power to coordinate the devices. As more and more devices are connected to power distribution networks, the rewards for coordinating their use grows greatly, yet the difficulties in monitoring and coordinating them similarly grows.
Therefore, there exists a need for an improved method of controlling these devices. In particular, there is a need for an improved method for co-ordinating smart devices to supply and/or draw power from power distribution networks.